2022 年 94 巻 8 号 p. 472-481
In this study, SEM-EDS analysis was applied to the measurement of the contamination percentage of artificial sand in recycled sand as follows. (1) For the count number-based contamination percentage measurement, the number of mixed-sand particles nnec necessary for achieving accuracy Δpnec was formulized by an equation : Δpnec was assumed to be a confidence interval width in statistics, and a true value of contamination percentage ptrue was used as a parameter. Next, by using mixed sands to resemble recycled sands, contamination percentages were experimentally measured by varying of ptrue and nnec values. The measured contamination percentages agreed very well within the confidence interval width Δpnec derived from the equation, which shows the effectiveness of the equation. (2) The contamination percentages by count number were transformed into those by mass% as follows. First, using EDS mapping images, the cross-sectional areas of particles on a polished surface were converted into diameters of equivalent-area circles. Secondly, approximating the sand particles as sphere, the diameters on polished surfaces were furthermore converted into orthogonal projective diameters of spheres. Thirdly, using the orthogonal projective diameters, the volumes of sand particles were calculated, and were multiplied by true densities. Finally, the volumes of sand particles were accumulated for all the exposed artificial and silica sand particles to estimate the contamination percentage of artificial sand by mass%. The estimated contamination percentages by mass% more or less agreed with the several compounding values. As a result, it was confirmed that the SEM-EDS analysis-based measurement method is effective when there is no significant difference in the grain size distributions, which was evaluated using AFS Grain Fineness Number (AFS GFN) in this work, between silica sand and artificial sand. The method should be further studied focusing on the large differences between the AFS GFNs.